By now, you've formed an opinion on Katy Perry's new single "Roar," but what does Katy's boyfriend John Mayer think about the song?  Unsurprisingly, he claims he knew it was a smash as it was being recorded.

Speaking to Billboard, John says, "I remember hearing it, going like, 'Wow what an interesting experience' to hear something that you identify as massive before it's massive."  Noting that he felt that "Roar" would be a "megaton bomb"-sized hit, he adds, "I thought it was a really sweet, unforgettable sort of experience" to hear Katy's song in the process of it being created.

"In a way you get swallowed up by it, it's so big," John says. "It's such an incredibly big song that it doesn't need you to tell anybody, while you're eating lunch, [that] millions of people are going to be dancing on tables to that."

As for "Who You Love," the duet he recorded with Katy for his own album, John tellsBillboard that he primarily wanted her to sing on it, not because she's his girlfriend, but because she has "a cool voice" and "a cool artistic personality."

In the song John talks about how he's "tried to run" from love in the past, but he's "not running anymore."  Katy, meanwhile, sings about how she didn't see John coming, and that people say "his heart's too hard to hold."

John reveals that Katy wrote her own verse for the song.  "It was a really fun opportunity for her to write like, her answer to that," John says. "So you get these two sides to this relationship that are brutally honest but no less universal."

John's album Paradise Valley comes out next week.  Katy's album is due in October.

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